In the reciprocating compressors with a linear motor, the gas compression mechanism occurs by the axial movement of approximation and spacing of a piston inside a cylinder, in relation to a cylinder head, which is mounted to an end of the cylinder and in which are positioned suction and discharge valves for controlling the gas inlet and gas outlet in the cylinder.
The piston is driven by an actuator, which carries a magnetic component driven by a linear motor. The piston is connected to a resonant spring and forms with the latter and with the magnetic component the resonant assembly of the compressor. This resonant assembly driven by the linear motor has the function of performing a linear reciprocating movement, making the movement of the piston inside the cylinder exert a compression action on the gas admitted by the suction valve, until said gas is discharged through the discharge valve to the high pressure side of the refrigeration system to which the compressor is mounted.
Variations in the operating conditions of the compressor, or variations in the voltage supply thereof may cause the resonant assembly to be displaced beyond a certain predetermined limit, from which the gas mass of the dead compression volume still existing in the compression chamber begins to actuate as an extra impeller to the piston, increasing the amplitude of its operating cycle, and making the piston top collide with the cylinder head, causing damages to the compressor.
Several forms of controlling the amplitude of the piston stroke have already been presented, either electronic (U.S. Pat. Nos. 5,156,005; 5,342,176; 5,496,153; 5,450,521; 5,592,073), which control the current supplied to the motor as a function of the piston position, or mechanical (usually employed in Stirling machines), such as the inclusion of relief gas channels, or mechanical or pneumatic springs. Electronic commands, which are able to precisely control the position of the piston, are extremely expensive, besides presenting an inertia that is inherent to the system, as it occurs with the mechanical solutions. Such inertia allows the occurrence of occasional impacts.